Dyeing of anodised aluminium

ABSTRACT

A PROCESS FOR DYEING ANODISED ALUMINIUM WHICH COMPRISES IMMERSING FRESHLY ANODISED ALUMINIUM IN A DYEBATH COMPRISING A BOILING SOLUTION OF A DYESTUFF IN A HALOGENATED HYDROCARBON SOLVENT OR A BOILING EMULSION OF A DYESTUFF, IN A HALOGENATED HYDROCARBON SOLVENT FOR EXAMPLE AN EMULSION OF AN AQUEOUS SOLUTION OF THE DYESTUFF IN THE HALOGENATED HYDROCARBON SOLVENT.

United States Patent 3,707,394 DYEING 0F ANDDISED ALUMINIUM John Joseph Clementson and Dennis Ward Glen, Runcorn, England, assignors to Imperial Chemical Industries Limited, London, England No Drawing. Filed Oct. 19, 1970, Ser. No. 82,213 Claims priority, application Great Britain, Oct. 27, 1969, 52,449/69 Int. Cl. C23f 5/04, 7/06 US. Cl. 117-127 8 Claims ABSTRACT OF THE DISCLOSURE A process for dyeing anodised aluminium which comprises immersing freshly anodised aluminium in a dyebath comprising a boiling solution of a dyestuff in a halogenated hydrocarbon solvent or a boiling emulsion of a dyestuff, in a halogenated hydrocarbon solvent for example an emulsion of an aqueous solution of the dyestuff in the halogenated hydrocarbon solvent.

This invention relates to a process for dyeing anodised aluminium.

It is well known to treat aluminium which is to be used for example in building structures to form a layer of aluminium oxide on the surface of the aluminium, and subsequently to dye the aluminium to improve its appearance. A conventional method of forming the aluminium oxide layer is to employ the aluminium as the anode of a direct-current electrolytic cell, particularly one in which the electrolyte is dilute sulphuric or chromic acid and the cathode is lead or steel respectively. An alternative electrolytic method of forming the aluminium oxide layer is to employ the aluminium as the anode of an electrolytic cell of which the electrolyte is oxalic acid and the cathode is carbon, iron, lead or stainless steel; such electrolytic cells may be operated using direct current or alternating current.

The material resulting from the above electrolytic processes is commonly known as anodised aluminium and is referred to as such herein.

Dyeing of anodised aluminium is normally effected immediately following the anodising treatment and comprises immersing the anodised aluminium, without first drying it, in an aqueous dyebath at a temperature of up to 100 C., but usually at a temperature of 50 C. to 65 C. The dyeing process is completed by contacting the anodised aluminium with steam or by immersing it in boiling water, in a heated solution of one or more metal salts for example nickel acetate or cobalt acetate, or in a solution of lanolin. These treatments have the effect of sealing the surface of the anodised aluminium.

However, the dyes having the best colour and light fastness properties are not sufficiently soluble in water to be applied by this method. It has therefore recently been proposed to dye anodised aluminium with acetonesoluble dyes from an acetone-based dyebath rather than from water, thus enabling to be used Water-insoluble dyestuifs which exhibit a high degree of resistance to weathering. In this acetone-based dyeing process the dyebath is employed at room temperature and preferably a subsequent treatment is employed to seal the surface of the anodised aluminium.

We have now found that freshly anodised aluminium can be effectively dyed from a dyebath comprising a ice halogenated, and particularly a chlorinated, hydrocarbon solvent.

According to the present invention, therefore, we provide a process for dyeing anodised aluminium which comprises immersing freshly anodised aluminium in a dyebath comprising a boiling solution or dispersion of a dyestulf in a halogenated hydrocarbon solvent.

Dyestuffs which are insoluble in the halogenated hydrocarbon solvent may be dispersed in the solvent and in particular an aqueous solution of the dyestulf may be dispersed (or emulsified) in the solvent. Thus there may be employed dyestufiis which are insoluble in the halogenated hydrocarbon solvent as Well as dyestuffs which are soluble. Any dyestuff may be employed which is useful in the conventional aqueous dyeing process (although the concentration of the dyestuif may vary according to the particular dyestufi used) as may any dyestulf which is useful in the known acetone-based dyeing process and which is at least partially soluble in the halogenated hydrocarbon solvent.

Freshly anodised aluminium on emerging from the anodising treatment is rinsed with water after the anodising treatment and preferably is dried prior to or simultaneously with dyeing it by the process of the invention. Drying may be effected as in the known acetone-based process by means of dry, warm air but we have found that a particularly suitable drying process for use in association with our dyeing treatment is a drying process which employs a drying agent based on a halogenated hydrocarbon solvent. Examples of halogenated hydrocarbon solvent-based drying agents which may be employed are solutions of cationic surface-active agents in trichloroethylene as described in British patent specification No. 835,072. Alternative drying agents based on a halogenated hydrocarbon solvent are solutions in a fluorochlorohydrocarbon solvent of a sodium, ammonium or amine salt of a monosulphonic acid derivative of a diester of a succinic acid as described in UK. patent specification No. 1,157,- solutions in a fluorochlorohydrocarbon solvent of an amine salt of undecyl or tridecyl benzene sulphonic acid as described in copending application No. 3S,044/ 68, now abandoned; solutions in a chlorohydrocarbon of a metal, ammonium or amine salt of the monosulphonic acid derivative of a diester of a succinic acid as described in copending application No. 21,814/ 69, now US. Patent No. 3,074,135; and solutions in a chlorohydrocarbon solvent of a metal, ammonium or amine salt of an alkyl benzene sulphonic acid wherein the alkyl group contains from 7 to 14 carbon atoms as described in copending application No. 49,275/ 69, now US. Pat. No. 3,002,679.

Thus according to a further feature of the present invention we provide a process for dyeing anodised aluminium which includes the step of drying freshly anodised aluminium by immersing it in a driving agent comprising, a halogenated hydrocarbon solvent. Conveniently the halogenated hydrocarbon solvent of the drying composition is the same solvent as the halogenated hydrocarbon solvent of the dyeing composition.

The drying treatment of the present invention may be included as a separate step intermediate the anodising treatment and the dyeing treatment. However, we have found that a particularly advantageous technique is to immerse the freshly anodised aluminium, after rinsing, in a drying composition based on a halogenated hydrocarbon solvent in which the dyestutf has been incorporated.

Thus according to a particularly preferred feature of the present invention we provide a process for dyeing anodised aluminium which comprises immersing freshly anodised and rinsed aluminium in a composition comprising a halogenated hydrocarbon solvent, a surfactant and a dyestuff.

The amount of the dyestuff may depend on whether the dyeing treatment and the drying treatment are carried out separately or together. In the case where the dyeing treatment is carried out as a separate treatment following a drying process the amount of the dye will usually be from 0.01% to 5.0% and especially about 0.1% by weight based on the hlogenated hydrocarbon solvent. In the case Where the dyeing treatment occurs simultaneously with the drying treatment the amount of the dye will again be from 0.01% to 5.0% by weight based on the halogenated hydrocarbon solvent, but in this case the preferred amount is greater than 0.1% and in particular is about 0.2% by weight. Also, in the case where an emulsion of the dyestuff in the halogenated hydrocarbon solvent is employed, the dyestutf tends to cause separation of the phases of the emulsion and for this reason we prefer to employ low concentrations of the dyestuif, for example about 0.2% by weight, in such emulsions. In the case where the dyebath is also to be used to dry the anodised aluminium the amount of the surface-active agent in the dyebath is usually only low, for example about 0.03% by weight, but if desired large amounts of this agent, for example up to 3% by weight, may be present. We have found that the surface-active agent competes with the dyestutf for the active sites on the anodised aluminium and for this reason we prefer to employ the minimum amount of the surface-active agent consistent with emulsification of the dyestufi? and with effective drying (if appropriate) of the anodised aluminium.

The halogenated hydrocarbon solvent is employed, at least in the dyebath, at the boil. Trichloroethylene or perchloroethylene are preferred solvents although the present invention is not limited in respect of the halogenated hydrocarbon solvents which may be employed and examples of other solvents which may be used are 1,1,1-trichloroethane, 1,1,2-trichloro-1,2,2-tri-fiuoroethane and methylene chloride. The solvent will usually contain stabilising additives to inhibit its degradation.

The time for which the anodised aluminium is immersed in the dyebath is not critical but will usually be at least minutes. For any particular anodised aluminium the depth of shade obtained generally increases as the time of immersion in the dyebath increases. Other criteria which affect the depth of shade are the concentration of the dyestuff in the dyebath and the thickness of the aluminium oxide layer, and the amount surfaceactive agent.

After the anodised aluminium has been dyed according to the present invention it will usually be rinsed in a boiling halogenated hydrocarbon solvent (which will usually be the same as the solvent employed in the dyebath). Immersion of the dyed material in the boiling solvent for example for 10 minutes is sufficient to seal the surface and we have found that it is not subsequently necessary to immerse the dyed material in boiling water or steam, although such a treatment can be included if desired.

The dyeing process of the invention has the advantages over the conventional aqueous dyeing process that it enables water-insoluble dyestuffs as well as water-soluble dyestuffs to be applied to anodised aluminium (thereby improving the weathering properties of the dyed material) and that it obviates the need for a consequent sealing treatment with, for example, boiling water or steam. The process has the advantage over the proposed acetonebased dyeing process that it employs a non-flammable solvent of low toxicity and in the preferred embodiment it obviates the need for a separate drying step; moreover it obviates the need for a sealing treatment in hot water or steam as is usually carried out in the acetone-based process.

Anodised aluminium is dyed by the process of the present invention to uniform shades and the colour is resistant to rubbing and to washing in hot or cold water, acetone or boiling trichloroethylene. The dyed material may be employed in any instances where anodised aluminium is conventionally used.

The invention is illustrated but in no way limited by the following examples:

EXAMPLE 1 A sheet of essentially pure aluminium measuring approximately 2" x 4" was made the anode of a DC. electrolytic cell having a lead cathode and comprising 15% v./v. sulphuric acid as electrolyte. The cell was maintained at 20 C. and a potential of 15 volts was applied across the electrodes for a period of 40 minutes.

The resulting anodised aluminium sheet was then rinsed in clean, cold water after which it was dried by immersing the wet sheet in a boiling solution of cetyl pyridinium bromide in trichloroethylene. After drying, the sheet was immersed for 10 minutes in a boiling solution (0.1% w./w.) of Waxoline Red 0 Dyestuff (C.I. 26105) in a commercially available grade of stabilised trichloroethylene. The dyed anodised aluminium was finally rinsed in clean, boiling trichloroethylene for 10 minutes to remove excess, unadsorbed dyestuff.

The anodised aluminium was dyed to an even, uniform orange shade and was completely free from stains and streaks. The orange colour was not removed and its shade was not changed by rubbing the dyed sheet with a variety of solvents including hot and cold water, acetone and trichloroethylene.

EXAMPLE 2 A sheet of essentially pure aluminium was anodised and subsequently rinsed in clean, cold water by the procedure outlined in Example 1. The resulting wet anodised aluminium was immersed in a boiling solution containing 0.075% w./w. cetyl pyridinium bromide and 0.2% w./w. Waxoline Red 0 Dyestuff in a commercially available grade of stabilised trichloroethylene for a period of 10 minutes. The Water on the anodised aluminium was removed in the form of a constant boiling mixture with trichloroethylene; the resulting vapours were condensed and the condensate was separated in a gravity-type separator to recover the trichloroethylene. The dyed anodised aluminium was then rinsed in clean, boiling trichloroethylene for 10 minutes to remove any residual traces of cetyl pyridinium bromide and any excess, unadsorbed dyestuff. The results were identical to those described in Example 1.

EXAMPLE 3 The procedure of Example 2 was repeated except that 0.1% W./w. sodium di(methylamyl)sulphosuccinate was employed instead of 0.075% w./w. cetyl pyridinium bromide and the concentration of Waxoline Red 0 was reduced to 0.1% w./w.

The results were the same as described in Example 1.

EXAMPLES 4-26 The procedure outlined in Example 2 was employed to dye freshly anodise'd aluminium using the dyebaths shown in Table 1 below. In each experiment the aluminium was dyed to a uniform shade which was unchanged by rubbing with hot or cold water, hot or cold acetone and hot or cold halogenated hydrocarbons.

TABLE 1 Surfaceactive agent 1 Example Dyestufi 1 Colour (0.03% No. Solvent (0.2% w./w.) index w./w.)

4 Triehloroethylenann I A 5-.- .-do I B A A B A do IV B 16 1,1,1-trichloroethane- Waxoline 0.1. B

Red 0. 26105 17 do Lithofor C.I.

Yellow A. 21240 18 Methylene eh1oritle. I B 19 do Waxoline C.I. B

Purple A. 60725 20 d0 IV 21 1,l,2-triel11oro-1,2,2-

trifiuoroethane. 22-- o 23 do Waxolme 24 Perchloroethylene I B 25 do II C 26 do III B 1 The dyestufis identified in the table by a. reference number were:

I= 1:4-bis(p-n-butylanalino)-5:8-dihydroxy antliraqulnone; II 1: 4-bis(isopropylamino) -anthraquinone; III l-amino--hydroxyanthraquinone; IV l-amino-2-methyl anthraquinone. 1 The surface-active agent was:

A=cetyl pyridinium bromide (Fixanol C); B=sodium di(methylamyl) sulphosuccinate (Manoxol MA); G=a lauryl derivative of a cyclic amine (Imidrol LC).

EXAMPLES 27, 28 and 29 A clear emulsion was prepared to the formulation:

Parts by weight Freshly anodised and rinsed aluminium prepared as in Example 1 was immersed whilst still wet in the boiling emulsion for a period of 15 minutes after which time it was withdrawn and rinsed by immersion for 10 minutes in an emulsion of the above formulation, but excluding the dyestuif. The aluminium was then rinsed in boiling trichloroethylene for 10 minutes.

In each experiment the anodised aluminium was dyed to a uniform shade which was not changed by rubbing with hot and cold water, hot and cold acetone and hot and cold trichloroethylene.

We claim:

1. A process for dyeing anodised aluminium which consists of immersing freshly anodised aluminium in a boiling dyebath consisting essentially of a halogenated aliphatic hydrocarbon solvent containing one or two carbon atoms in which is incorporated a member of the class consisting of a dyestutf and an aqueous solution of a dyestutf, and from 0 to 3% by Weight of a surface active agent based on the hydrocarbon solvent and rinsing the dyed anodised aluminium subsequent to its withdrawal from the dyebath in a boiling halogenated aliphatic hydrocarbon solvent containing one or two carbon atoms to seal the dyed anodised aluminium.

2. A process as claimed in claim 1 wherein the dyestulf is soluble in the halogenated hydrocarbon solvent.

3. A process as claimed in claim 1 wherein the dyebath comprises an emulsion in the halogenated hydrocarbon solvent of an aqueous solution of the dyestuif.

4. A process as claimed in claim 1 wherein the anodised aluminium is dried prior to immersion in the dyebath by immersion in a drying agent comprising a halogenated aliphatic hydrocarbon solvent containing one or two carbon atoms and up to 3% by Weight based on the hydrocarbon solvent of a surface-active agent.

5. A process as claimed in claim 1 wherein the amount of the dyestuft' is from 0.01% to 5.0% by weight based on the halogenated hydrocarbon solvent.

6. A process as claimed in claim 1 wherein the halogenated hydrocarbon solvent is trichloroethylene.

7. A process as claimed in claim 4 wherein the surfaceactive agent in both the drying agent and the dyebath is cetyl pyridinium bromide.

8. A process as claimed in claim 1 wherein the freshly anodised aluminium is rinsed and directly immersed in the boiling dyebath.

References Cited UNITED STATES PATENTS 3,440,111 4/ 1969 Dale 1486.1 3,447,953 6/1969 Gebauer et al. 204-35 N X 3,012,917 12/1961 Riou et a1 148-627 X 3,019,143 1/ 1962 Dessauer 148-6.1

RALPH S. KENDALL, Primary Examiner C. WESTON, Assistant Examiner US. Cl. X.R. 

